Extinct Red Sea Brine Pool Reveals Pre-Oxygen Life Mechanisms

Researchers have identified evidence of a once-active, now-extinct brine pool in the Red Sea that may explain how primordial life survived before atmospheric oxygen became abundant. The findings challenge previous assumptions about deep-sea salt lakes, which marine ecologists historically labeled “black pools of death” due to their perceived lack of oxygen. Despite this reputation, biologists have long observed extremophiles thriving along the margins of these teal-colored undersea formations.

Survival Before Oxygen Abundance

The new study, published in AGU Advances, indicates that specific microbial species inhabited the extinct Hume pool between roughly 2,000 and 16,000 years ago. These organisms, including novel forms of Myxococcota phylum “slime bacteria” and the genus Nitrospira, appear to oxidize free-floating manganese and iron into minerals. According to the team, this metabolic process represents “an early mechanism for energy production in Earth’s pre-Great Oxidation Event.” Such activity may have set the stage for the massive influx of oxygen into the atmosphere from the oceans between 2.4 and 2.1 billion years ago.

Expeditions and Site Analysis

Morgan Chakraborty, a PhD candidate in marine geosciences at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science, led the work alongside advisor Professor Sam Purkis and colleagues from the nonprofit OceanX. The investigation relied on data collected by the research vessel R/V OceanXplorer and its Mariner XL Argus remotely operated vehicle (ROV). Between 2020 and 2023, three expeditions examined five distinct brine pools.

Two sites proved critical: the active NEOM pool located approximately 5,807 feet (1,770 meters) below sea level in the Gulf of Aqaba, and the Hume pool situated 4,495 feet (1,370 meters) deep in the northern Red Sea rift. While NEOM remains an active brine lake, the Hume site lacks the liquid brine itself but retains structural hallmarks of such formations. The researchers classified Hume as an “extinct pool” based on sedimentary layers rich in calcium-carbonate skeletons of tiny multicellular metazoans and a “radically discolored ‘beach’” similar to the microbial zones surrounding NEOM.

Geochemical and Genetic Findings

The project was driven by marine geoscientists rather than biologists, focusing on sediment samples mixed with organic matter from both locations. At Hume, these samples contained echinoderm skeletons and other micro-fossils. For the active NEOM pool, the team deployed metagenomic techniques to analyze the DNA of living extremophiles. Subsequent metatranscriptomics revealed how these genes express themselves, showing that microbes like those in the Candidatus Brocadiae grouping harvest and oxidize minerals to generate energy without robust access to oxygen.

Geochemical analyses further demonstrated that sediments within these brine pools are rich in metallic elements, including manganese, iron, molybdenum, and copper. Concentrations of these metals sometimes exceed levels found in surrounding sediments by more than 100 times. The researchers suggest these microbes act as natural accumulators of precious metals. “[Many] of these metals are essential for clean energy technologies, and understanding how they accumulate could help guide future resource exploration,” the study authors explained. They added that similar processes likely occurred in other ancient salt giant basins.